In recent years, highly functional optical film provided with such as an antireflection function and a hard coat function is required in accordance with full colorization of a note personal computer and a cell phone, and higher precision requirement for a display. Recently, to improve visual recognition property, it has been required to provide the surface with such as antireflection property and anti-stain property; and, for example, developed has been optical film having a functional layer comprising such as metal oxide on cellulose ester film directly or intervening another layer. Further, the thinner layer thickness of utilized film is required to realize a thinner display apparatus, or the larger width of optical film is required to realize a larger image plane. Particularly with respect to a large image plane, optical film having excellent flatness is required; however, conventional film cannot achieve excellent flatness and has a problem of haze generation particularly in the case of a large width and a thin layer thickness.
Generally, additives such as a plasticizer and an ultraviolet absorbent are contained in cellulose ester film. These additives are added to improve processing behavior and moisture permeability of cellulose ester film However, on the other hand, by incorporation of these additives, there was a problem of deterioration in coating behavior at the time of arranging various coating layers on cellulose ester film.
In particular, there was a problem of change in physical properties due to bleed out or evaporation of these additives resulting in deterioration of storage stability and haze of cellulose ester film before processing.
To overcome these problems, accumulated type cellulose ester film by means of a co-extrusion method to provide distribution along the thickness direction, with respect to an incorporation method of a plasticizer and an ultraviolet absorbent, has been disclosed (for example, refer to patent documents 1 and 2). Further, such as a method to change types of a plasticizer, to utilize a new plasticizer or to incorporate plural types of plasticizers has been disclosed (for example, refer to patent documents 3-5). However, it is a present state that the effect is limited in the case of film having a large width and a thin layer thickness, and improvement of flatness and haze is insufficient.
Further, at the time of forming a hard coat layer on the aforesaid cellulose ester film, generally, a curable substance layer which is cured by actinic rays such as ultraviolet rays is coated and cured by irradiation of actinic rays. At this time, when flatness deterioration or bleed out is present in cellulose ester film as a substrate, there was a problem of generation of coating unevenness to further deteriorate flatness in accordance with curing shrinkage of a hard coat layer by irradiation of actinic rays. The phenomenon was particularly significant with cellulose ester film having a large width.
Further, in the case of coating an antireflection layer on a hard coat layer to prepare antireflection film, the aforesaid flatness deterioration will deteriorate the antireflection function itself and handling characteristics, which will be a cause to generate light leakage, visual recognition deterioration and color shading when said antireflection film is utilized in a polarizing plate or a display apparatus, and desired has been cellulose ester film having excellent flatness and haze even when a hard coat layer or an antireflection layer is provided.
[Patent Document 1] JP-A 2001-131301 (JP-A refers to Japanese Patent Publication Open to Public Inspection No.)
[Patent Document 2] JP-A 2002-90544
[Patent Document 3] JP-A H11-246704
[Patent Document 4] JP-A 2001-247717
[Patent Document 5] Japanese Translation of PCT International Application Publication No. 2005-515285